The process for making a plastic container by blow molding a tubular parison preferably of extruded thermoplastic material comprises guiding a tube into a divided open blow mold, closing the blow mold and feeding pressurized air into the tubular parison squeezed off in the blow mold.
Further in the open blow mold which has a suitable receptacle, at least one single-piece hoop ring made of thermoplastic material with appropriate tolerances by injection molding is mounted on the tube and bonded with the tubular parison in the blow molding.
There is a problem with the known steps of the known process over which our invention is an improvement.
A container ring which is bonded with the container outer surface of the finished container has tolerances in the plane of the ring which are distributed statistically and are characterized as use tolerances and can amount to a few millimeters. This is troublesome and can lead to rejection and waste inasmuch as the container ring simultaneously is part of a sealing closure device which comprises an opposing ring on an associated container cover and a clamping ring or the like.
Because of the described use tolerances the closure device may not be able to satisfactorily seal.
To eliminate this disadvantage, container rings made by injection molding but sorted carefully to be sufficiently planar and thus free of use tolerances are usually used in the manufacturing process for the plastic container. That is expensive.
In addition, disturbing variations occur even when the container rings are carefully selected in this described way. The container ring can also have deviations from a truly circular shape and those that do must also be sorted out if this method is used.